The present invention relates to the field of interventional cardiology and, more particularly, to a catheter and a related method for the ablation of atrial flutter utilizing radio frequency energy.
Many advances have been made in interventional therapy for cardiac arrhythmias, as devices such as catheters for mapping and ablation of target areas have improved. Many arrhythmias are now frequently treated by using specially adapted radio frequency (RF) catheters. The successful treatment rate of RF catheters may reach  greater than 90% for certain cardiac arrhythmias. Moreover, RF ablation using a catheter does not require general anesthesia and recovery from the procedure is rapid.
Electrical conduction problems such as ventricular tachycardia and artioventricular node reentrant tachycardia are also routinely treated without general anesthesia utilizing radio frequency ablation. However, for those patients in whom maintenance of sinus rhythm is not possible (approximately 20% of patients over 60 years old), control of ventricular rate is achieved with AV nodal blockers such as digoxin, xcex2-blockers, or calcium channel blockers. Although prior to the present invention, a xe2x80x9ccurexe2x80x9d of atrial fibrillation with catheter ablation techniques appeared not to be possible, various attempts had been made at permanent modification of the AV conduction such that rapid conduction could be eliminated, but normal conduction (fewer than 100 beats per minute) remains, thereby avoiding the need for a permanent pacemaker. Unfortunately, these attempts have been unsuccessful. See, Vogel and King, The Practice of Interventional Cardiology, 2nd Ed., pages 671-683 (1993).
Accordingly, specially adapted radio frequency ablation catheters designed for either general purpose or specific application are known in the art, some of which are widely used. For example, U.S. Pat. No. 5,507,802 to Irman, for xe2x80x9cMETHOD OF MAPPING AND/OR ABLATION USING A CATHETER HAVING A TIP WITH FIXATION MEANS.xe2x80x9d (Irman ""802) generally discloses a mapping and/or ablation catheter 11 having a flexible elongate tubular member 12, with a large central lumen 16 and a plurality of additional lumens 17 (see, column 2, lines 7-35). Anchoring or fixation means are carried by the distal tip 21 with means for selective engagement and disengagement of the fixation means. Irman ""802 also discloses plural ring platinum electrodes 46, 47 near the distal tip and conducting means 48, 49 which extend through the additional lumens of the catheter for connection to a remote source of radio frequency energy (see, column 3, lines 14-20).
U.S. Pat. No. 5,673,695 to McGee et al. for xe2x80x9cMETHODS FOR LOCATING AND ABLATING ACCESSORY PATHWAYS IN THE HEARTxe2x80x9d (McGee et al. ""695) discloses an ablation catheter having a multifunction element 40 (ring electrodes E1-E10) spaced apart and located near the distal tip for location/ablation of accessory electrical pathways of the heart (see, column 6, lines 7-52). The body 42 of the catheter can be constructed from a variety of flexible resilient materials and also may include an inner core of a suitable metal or super elastic material such as Nitinol(copyright) (see, column 5, lines 48-67).
U.S. Pat. No. 5,582,609 to Swanson et al., for xe2x80x9cSYSTEMS AND METHODS FOR FORMING LARGE LESIONS IN BODY TISSUE USING CURVILINEAR ELEMENTSxe2x80x9d (Swanson et al. ""609) describes generally the need for catheters designed especially for treatment of atrial fibrillation and atrial flutter, having xe2x80x9cthe larger ablating mass required for these electrodes among separate multiple electrodes spaced apart along a flexible bodyxe2x80x9d (see, column 1, lines 42-61). The ""609 reference discloses both spaced apart ring electrodes and coiled spring configurations (see, FIGS. 36, and columns 6-7) and at column 8, lines 23-31 further describes the use of a sliding sheath 50 (FIG. 12). However, this sheath 50 slides within the lumen of catheter body 12 and is used to vary the impedance and the surface area contact of the coil electrode 46. The ""609 reference specifically discloses the lesion patterns attainable with the device for treatment of atrial flutter and discloses how lesion characteristics can be controlled (see, column 9, lines 5-30).
U.S. Pat. No. 5,111,811 to Smits, for xe2x80x9cCARDIOVERSION AND DEFRIBRILLATION LEAD SYSTEM WITH ELECTRODE EXTENSION INTO THE CORONARY SINUS AND GREAT VEIN.xe2x80x9d discloses a screw anchor fixation assembly 76 having a rotatable corkscrew electrode 78 (see, FIG. 4 and column 6, lines 33-44.
U.S. Pat. No. 5,578,067 to Elkwall et al., for xe2x80x9cMEDICAL ELECTRODE SYSTEM HAVING A SLEEVE.BODY AND CONTROL ELEMENT THEREFOR FOR SELECTIVELY POSITIONING AN EXPOSED CONDUCTOR AREAxe2x80x9d discloses a sleeve like body 19 (sheath) having a window-like opening 18. The sheath 19 slides along the electrode cable 3 to vary the location of the exposed electrode 6a (see, FIG. 4, and column 5, lines 28-45).
Atrial flutter is a rapid abnormal rhythm of the atrium with the electrical impulse traveling around the orifice of the right atrium at the junction with the inferior vena cava, the major vein collecting blood from the lower body and returning it to the heart. This abnormal electrical impulse travels through a strip of heart muscle, termed the isthmus, located between this orifice and another orifice between the right atrium and right ventricle.
A total interruption of this pathway, i.e. the isthmus, by an interventional procedure such as RF ablation has been shown play a key role in successfully curing atrial flutter. The current technique utilizes a general purpose RF ablation catheter. The tip of the catheter is dragged across the entire width of the isthmus under fluoroscopic guidance to create a complete linear cut by RF energy. Using this technique requires a high skill level and may necessitate multiple attempts to achieve a proper cut. Thus, the procedure may be time consuming and result in heavy X-ray exposure. Furthermore, its availability is limited to selected major medical centers having a large patient population.
As should be appreciated, creation of a consistent and complete linear lesion requires full and stable contact between the electrode and the endocardial surface along the entire length of the cut. Currently available catheters including those described in the above-cited patents lack the ability to maintain such contact without either dragging the catheter or repositioning it several times during the procedure. Therefore, the procedure remains time consuming and highly dependent on the operator""s skill level.
Accordingly, a need is identified for a radio frequency ablation catheter that is specially adapted for the treatment of atrial flutter that makes the treatment less time consuming and less dependent on the operator""s skill. The catheter would be flexible to facilitate the bending necessary to place the electrodes used for ablation over the target area for treatment. Anchoring means would also be included to anchor the catheter in position to facilitate the bending operation and to ensure that the catheter remains in the proper position over the target area during the procedure, thereby avoiding the need for dragging or repositioning of the catheter during the procedure. Overall, such a catheter would be simpler to operate and thus require a lower skill level to successfully perform the ablation procedure.
It is a primary object of the present invention to provide a radio frequency ablation catheter and a related method of catheterization that overcomes the limitations and shortcomings of the above-referenced prior art devices and methods.
It is another object of the present invention to provide a radio frequency ablation catheter specially adapted for the treatment of atrial flutter that is simpler to operate, thereby making a successful outcome less dependent upon the skill of the operator.
Another object of the invention is to provide a catheter electrode for the purpose of ablative procedures using radio frequency energy that is more flexible than those presently available.
Yet another object of the invention is to provide an anchoring device at the distal end of the catheter to ensure that stable contact with the target cardiac tissue is maintained.
A further object of the invention is to provide a catheter wherein the ablation electrodes are positioned in the middle portion of the catheter, rather than at the distal end, said electrodes including multiple closely spaced ring electrodes or a long spring coil electrode for creating a linear lesion along the entire length of the cut line, i.e., over the entire isthmus.
It is also an object of the invention to provide a pre-shaped semi-rigid guiding sheath to assist in molding the contact portion of the catheter.
A further object of the invention is to provide a catheter having a removable stylet and corkscrew anchoring means coupled with a flexible electrode, shaft and a pre-molded sheath that is specific for ablative treatment of atrial flutter.
Additional objects, advantages and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as described herein, an electrode catheter is provided having a predetermined flexibility throughout the entire length or at least at the contact portion, such as the electrode region. This flexibility advantageously allows for the molding of the contact portion such that it conforms to the shape of the heart at a preselected desired target area, such as the isthmus between the inlet of inferior vena cava and posterior tricuspid annulus. Moreover, the flexibility of the catheter allows the operator to maintain steady contact with the target area for delivering radio frequency energy, thereby reducing the operator skill level necessary for performing the ablation procedure.
In one embodiment, the device of the invention comprises either a flexible multipolar or monopolar electrode of a ring or spring coil configuration. These ablation electrodes are positioned in the middle portion of the catheter, i.e., away form the distal portion (as with currently available catheters), to ensure proper positioning over the target area (which as described below is primarily the cardiac isthmus). Preferably, the most distal portion of or ring forming the electrode is mounted approximately 10 cm from the end of a hollow tube catheter having a sealed distal end. Advantageously, the spaced ring or spring coil electrode configurations work in conjunction with the flexible tubular body to allow the catheter to freely bend. While the catheter body is made of flexible material that resists a predetermined amount of tension, it is in general is not freely stretchable. The catheter body is also electrically insulating and is preferably constructed from a biocompatable material, such as polytetrafluoroethylene (PTFE), that is non-thrombogenic and can resist sustained heat of up to 100xc2x0 C.
The ring or spring coil electrodes are attached to at least one electric wire running through the lumen of catheter. Alternatively, the electric wire can be mounted within the body of the catheter and exteriorized at the proximal end for electrical connection to a recorder and a radiofrequency energy generator. The resistance of the connecting wires should be low enough to allow delivery of the energy up to 50 watts (or higher if such higher energy generator is approved by FDA) without creating heat or breaking insulation.
In accordance with an important aspect of the invention, a screw-in anchoring device or anchoring hook is located at the distal tip of the catheter. This device includes a corkscrew tip that is used to anchor the catheter at a preselected location during deployment, which advantageously allows the operator to bend or mold the catheter as necessary to place the electrodes at the desired target location.
Inside the catheter body is a lumen sized to accommodate a""stylet. The stylet provides some rigidity to the catheter during manipulation and deployment, which is similar to the technique used for implantation of a pacemaker electrode. In one embodiment, the stylet is configured with a means for remotely controlling the anchoring device provided at the distal tip of the electrode catheter. By using the stylet to control the anchoring device, removal or re-insertion of the catheter at any time during an ablation procedure is possible, as may be necessary for use in particular circumstances.
The hollow tube-like member forming the catheter body is preferably supported by a metallic spring coil to maintain the desired flexibility. In addition to providing support, this spring coil aids in supporting and reduces the incidence of kinking without sacrificing flexibility. The spring coil is preferably embedded in the wall of the catheter.
In accordance with another important aspect of the present invention, a guiding sheath is provided to assist in molding the electrode portion of the catheter over the isthmus during deployment. The sheath is preferably semi-rigid and pre-shaped with a bend or angulation. As described further below, the sheath fits over the catheter and allows it to be molded in vivo to ensure that stable contact is made with the target treatment area.
As should be appreciated, the catheter of the present invention is designed primarily for use in radio frequency ablation procedures performed at the isthmus between the inlet of inferior vena cava and posterior tricuspid annulus for permanent treatment of atrial flutter in human subjects. More particularly, the objective of the specially designed devices described herein is to increase the ease of use of the catheter in performing such a procedure while achieving a high success rate. For instance, using the presently proposed catheter, manipulation/positioning of the catheter during its deployment is much less dependant on the skill and dexterity of the operator because of the combined function of the anchoring device and preshaped guiding sheath. Therefore, the time required to complete the ablation procedure and the concomitant X-ray exposure is much less than that associated with conventional ablation devices, yet the high success rate of the procedure is maintained even in the clinical electrophysiology laboratory of an average size.